The technique of hydrating alkylene oxides to produce alkylene glycols is known. In particular, the production of ethylene glycol by the hydration of ethylene oxide is being conducted at a large scale. However, in conventional techniques, undesirable by-products such as dialkylene glycols and trialkylene glycols are produced besides alkylene glycols. In order to inhibit the generation of such by-products to thereby heighten selectivity for alkylene glycols, water should be used in an amount as large as from 10 to 20 times that of the alkylene oxides. Use of such a large amount of water is undesirable from the standpoint of water removal at a purification step. Use of various catalysts for improving selectivity has been investigated as a means for eliminating the above problem, and many reports have been made thereon.
Although it is known to use an acid or base alone as a catalyst, this technique is insufficient in selectivity improvement.
JP-A-51-127010 discloses the use of a combination of an organic base and carbon dioxide as a catalyst. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) As the organic base is used a tertiary amine.
JP-B-49-24448 discloses the use of a combination of an alkali halide or ammonium halide and carbon dioxide as a catalyst. (The term "JP-B" as used herein means an "examined Japanese patent publication".)
JP-B-60-45610 discloses the use of a molybdic acid salt as a catalyst.
JP-B-60-45611 discloses the use of a tungstic acid salt as a catalyst.
However, these conventional catalysts have a drawback that they dissolve in the reaction mixture and are hence difficult to recover therefrom. Several reports have hence been made on a technique for fixing the active ingredients of such conventional catalysts.
JP-B-60-56141 discloses the use of a combination of an anion-exchange resin which has undergone exchange for halogen anions and carbon dioxide as a catalyst.
JP-B-5-47528 discloses the use of a solid support, as a catalyst, which has an anion-exchanging ability and has undergone exchange for metal oxide anions such as molybdate ions, tungstate ions or vanadate ions. As the solid support is used an anion-exchange resin.
EP-A-741,683 discloses the use of a solid, as a catalyst, which has an anion-exchanging ability and has undergone exchange for hydrogencarbonate ions, hydrogensulfite ions, carboxylate ions or the like. As the solid is used an anion-exchange resin.
However, anion-exchange resins generally have low heat resistance, and the conventional catalysts each based on an anion-exchange resin do not necessarily have a sufficient catalytic life.